Reply To: MPCNC 2.8w $100 laser add-on complete

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LOL, Yes, I work as a quality engineering technician so I’ve written a few work instructions for sure:) As far as your question goes, I’m not familiar with the JTP driver but measuring current with a meter directly across the output terminals (dead short) is not a good idea . If you tried that with the Chinese driver you’d probably blow the fuse on your meter or maybe fry it before you got anywhere near the 1.8 amp target. Measuring DC current in series with the load is pretty standard practice.

The JTP driver probably has some cool fool-proofing circuitry that allows this, just like it can accept control signals from 3.3V TTL all the way up to the 12V found on the Ramps fan terminals. Their circuit brings the level up or down automatically which is nice. JTP is the Mercedes and I’m writing for the Kia crowd.

I think Villamany designed some type of current meter for his 3dpburner project so you can check it out over there. I think he mentions something about avoiding installation inline with the laser because he was worried voltage spikes from the capacitors would fry the laser diode. With some components built in to trap voltage spikes , it should work just fine as a real time laser output current monitor though.

The firmware change only takes a couple of minutes but is actually not necessary. You can use the D9 fan output but it you’d have to connect it to a simple voltage divider circuit to bring it down from 12v to 5v. I would’ve done this but I’m impatient and now that Radio Shack is gone (R.I.P), there is no place for me to go to get resistors quickly. You can use a 10k and 7k resistor to get you very near 5v or use a voltage divider calculator to come up with different values.